RE: [SECMECH] Framework Bindings Vs. Mechanism Bridges

Bernard Aboba <aboba@internaut.com> Fri, 26 August 2005 15:15 UTC

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Date: Fri, 26 Aug 2005 08:14:54 -0700 (PDT)
From: Bernard Aboba <aboba@internaut.com>
To: Charles Clancy <clancy@cs.umd.edu>
Subject: RE: [SECMECH] Framework Bindings Vs. Mechanism Bridges
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> I think EAP-Kerberos should be terminated at the AAA server.  Your service
> ticket is for "network access", not a particular NAS.  The key contained
> within the service ticket could be used to bootstrap the traditional EAP
> keying.  If you wanted fast reconnect or fast handoff, you could build it into
> the method by computing something like:
> 
> initial key generation:
> MK = PRF(service key, "master key", nonces)
> MSK_1 = PRF(MK, "master session key", nonces)
> 
> handoff:
> MSK_2 = PRF(MK, "new master session key", MSK_1 + nonces)
> 
> Then the NAS doesn't need to know anything about Kerberos.

This scheme allows for reuse of the initial Kerberos ticket, at the 
expense of a round-trip between the NAS and AAA server on each handoff. 

However, the Kerberos session key is no longer bound to a 
particular NAS -- this is the "Key binding" requirement in 
draft-housley-aaa-key-mgmt-00.txt.  

Also, the AAA server now needs to keep a cache of Kerberos session keys.  

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